Irrigation of crops by implanting porous plastic tubing in the soil and pumping water and nutrients into the tubing, which then permeate into the soil, is known. The water and nutrients pass through the walls of the tubing into the ground and irrigate and fertilize the crops.
A. A. Stone and H. E. Gulvin, in "Machines for Power Farming," Third Edition, John Wiley and Sons (1977) p. 188, describe apparatus for laying flexible plastic pipe into the soil comprising a subsoiler unit pulled by a tractor and pulling a mole behind the subsoiler. The mole is described to be oval-shaped, varying in diameter from 3-8 inches (7-20 cm). As the mole is pulled behind the subsoiler point, it leaves a tunnel which is said to have been known to last for up to eight years under "ideal" circumstances. To lay plastic piping, this article describes a method in which the pipe is drawn into a tube behind the shank of the subsoiler and is buried by the falling earth.
A problem which has existed using this prior method and apparatus is that most fields are often subjected to circumstances and conditions which are far from "ideal," and flexible tubing collapses under either the weight of the earth or the weight of heavy equipment riding over the soil above the tubing. When collapsed, the tubing can no longer be used and must be replaced. This invention overcomes this problem.